The invention relates to an expansible anchor for anchoring an article to a component, especially a concrete part.
An expansible anchor for anchoring of an article to a component, e.g. a concrete part, is known including a shank, which has means for fixing an article at its rear end and a portion of reduced cross-section near its front end with an adjoining expander cone, an expansible sleeve having longitudinal slits and positioned over the shank portion of reduced cross-section and locking elements projecting from the expansible sleeve beyond an outer diameter of the expansible sleeve.
Expansible anchors of this type are especially suitable for use in hard building materials. The expansible anchor is inserted with its front end first into a drilled hole in the component and the article is placed over the projecting rear end of the shank. By screwing a nut onto the threaded rear end of the shank projecting beyond the component and the article to be fastened to it, the expander cone integrally formed with the shank is drawn into the expansible sleeve bearing against the wall of the drilled hole. The expansible sleeve is braced in the drilled hole by locking elements provided on it, which catch against the wall of the drilled hole.
The expansible sleeve is normally rendered expansible by several longitudinal slits in it. The longitudinal slits create expansible arms, but at the rear end edge of the longitudinal slits the expansible sleeve has a closed sleeve shape. To expand the expansible arms it is therefore necessary to bend open the arms beyond a line connecting the ends of the two longitudinal slits defining the arms. A considerable expansion force is required for that purpose, depending first on a wall thickness of the expansible sleeve and second on the width of the arms and additionally their outer shape. A certain width of expansible arms is nevertheless required to achieve satisfactory holding forces with the expansible anchor.
By suitably matching the cone angle, it is possible to draw the expander cone into the expansible sleeve using a reasonable torque, in so doing expanding the expansible sleeve to effect anchoring. The resistance of the expansible arms to expansion is, however, too high to allow the expander cone to slide-up subsequently if the drilled hole should widen as a result of cracks forming. This inability of the expansible sleeve to expand subsequently means that the known expansion anchors are not suitable for use in the tensile zone in which cracks can form in a wall of the drilled hole as a result of tensile stresses occurring in the concrete. If the drilled hole enlarges because of crack formation, the expansible sleeve of the known expansion anchors is unable to compensate for this enlargement, so that even a light load causes the anchor to be pulled out of the drilled hole.